1. Field of the Invention
The present invention relates to a method of manufacturing an electrically rewritable phase change memory device for non-volatile memory storage of a resistance value determined by the phase change of a metal compound between a crystalline state and an amorphous state.
2. Description of the Related Arts
Non-volatile memory devices include those using a crystalline state and an amorphous state of a metal compound as memory information. As the memory material, tellurium compounds are generally used. The principle of storing information due to the difference of the reflectance thereof has been used generally in optical information memory media such as DVD (Digital Versatile Disk).
In recent years, it has been proposed to utilize the principle also for electric information storage. Different from the optical method, this is a method of detecting the difference of an electric resistance between amorphous and crystal, that is, a high resistance state of the amorphous and a low resistance state of the crystal, by the amount of current or the change of voltage. This is known as a phase change (type) memory and known technical documents include, for example, Patent Document 1 (U.S. Pat. No. 6,750,469). The present invention concerns the electrical information storage.
A basic structure of a memory cell of a phase change memory has a structure of a combination of a phase change resistance device and a selection device. The phase change memory stores and possesses information by forming a non-volatile recording material layer to a crystalline state or an amorphous state by a Joule heat generated by applying a current from a selection device to a phase change resistance device. Rewriting of the information may be attained by applying a high current to elevate the temperature of the resistance change material to a melting point or higher and then rapidly cooling the same, in a case where an amorphous state having electrically high resistance is formed. A crystalline state having an electrically low resistance may be attained by restricting the current to be applied so as to reach a crystallization temperature which is lower than the melting point. Generally, a resistance value of a no-volatile recording material layers changes from 2 to 3 digits by the phase change. Accordingly, in the phase change memory, a reading signal is different greatly depending on whether the state is crystalline or amorphous to facilitate the sensing operation.